COMBUSTION DIAGNOSIS DEVICE FOR INTERNAL COMBUSTION ENGINE

Abstract

A combustion diagnosis device for a diesel engine having a plurality of cylinders, including an engine speed sensor for detecting a rotational speed of each cylinder, an injection correction amount calculation unit for calculating an amount of correction for fuel injection of each cylinder in accordance with the engine speed sensor, a rotational fluctuation calculation unit for calculating a rotational fluctuation of each cylinder in accordance with the engine speed sensor, and a combustion state determination unit for determining a combustion state of a determination-target cylinder in accordance with the rotational fluctuation when the correction amount calculated by the injection correction amount calculation unit reaches an upper limit threshold value.

Description

TECHNICAL FIELD

The present invention relates to a combustion diagnosis device for an internal combustion engine having a plurality of cylinders.

BACKGROUND ART

In a diesel engine, an accumulator fuel injection device in which pumped fuel from a fuel tank is pressurized by a high-pressure supply pump, and in which pressurized fuel is injected from a compression chamber of a common-rail into a combustion chamber via a injector provided in each cylinder, for example, is known as a fuel injection device that is used in an internal combustion engine having a plurality of cylinders.

In the accumulator fuel injection device that includes the injectors provided in each cylinder, the fuel injection quantity that is injected and supplied from the injectors into each combustion chamber may become unstable (fluctuation), and so-called misfire phenomenon that prevents fuels from being ignited may be caused. Therefore, the fluctuation of explosion power in each cylinder or the deterioration of exhaust emission may be caused due to unstable combustion conditions of each cylinder, and as a result, the running performance of the diesel engine may be deteriorated.

For reducing the fluctuation of fuel injection quantities in each cylinder, so-called FCCB control (Fuel Control for Cylinder Balancing) that detects a rotational fluctuation of a crankshaft when the operational state of the diesel engine is in the stable state, and corrects the fuel injection quantity in accordance with the detected rotational fluctuation, is known (for example, refer to a patent document 1).

Further, a combustion diagnosis device for the internal combustion engine that determines the combustion state of the diesel engine in accordance with the correction amount of fuel injection quantity calculated by the FCCB control, is also known.

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: Japanese Patent Application Publication No. 2006-63824

Incidentally, in the above mentioned combustion diagnosis device that using a FCCB control, when a diesel engine receiving the effects of disturbances, a correction amount for a fuel injection quantity by the FCCB control has a tendency to be calculated in large amount. In a case where the combustion state of an internal combustion engine is determined without removing the effects of disturbances, the correction amount for the fuel injection may be calculated in large amount, and as a result, determination errors may be caused, though the combustion state of the internal combustion engine in fact is normal state.

The present invention has been designed in consideration of these problems, and an object thereof is to provide a combustion diagnosis device for an internal combustion engine having a plurality of cylinders with which the effects of disturbances are removed to accurately determine the combustion state of each cylinder.

Means for Solving the Problem

To achieve the object described above, a combustion diagnosis device for an internal combustion engine having a plurality of cylinders according to the present invention includes an engine rotational speed detection means for detecting the rotational speed of each cylinder of the internal combustion engine, an injection correction amount calculation means for calculating the amount of correction for the fuel injection of each cylinder in accordance with the engine rotational speed detection means, a rotational fluctuation calculation means for calculating the rotational fluctuation of each cylinder in accordance with the engine rotational speed detection means, and a combustion state determination means for determining the combustion state of a determination-target cylinder in accordance with the rotational fluctuation when the correction amount calculated by the injection correction amount calculation means reaches an upper limit threshold value.

Further, when the rotational fluctuation is larger than a determination threshold value of advanced angle injection timing, the combustion state determination means may determine the injection timing of the determination-target cylinder as an advanced angle side.

Further, when the rotational fluctuation is smaller than a determination threshold value of retarded angle injection timing, the combustion state determination means may determine the injection timing of the determination-target cylinder as a retarded angle side, and the determination threshold value of retarded angle injection timing is smaller value than the determination threshold value of advanced angle injection timing.

Further, when the rotational fluctuation is larger than a determination threshold value of misfire state, the combustion state determination means may determine that an misfire is caused in the determination-target cylinder, and when the rotational fluctuation is less than or equal to the determination threshold value of misfire state, the combustion state determination means may determine that the misfire is not caused in the determination-target cylinder.

The combustion diagnosis device for the internal combustion engine may further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

Further, when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means may correct the base fuel injection of each cylinder by previous correction amount.

Effect of the Invention

With a combustion diagnosis device for an internal combustion engine according to the present invention, the combustion diagnosis device that can accurately determine the combustion state of each cylinder by removing the effects of disturbances is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a combustion diagnosis device for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control unit of the combustion diagnosis device for the internal combustion engine according to this embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel injection timing determination control executed by the combustion diagnosis device for the internal combustion engine according to this embodiment of the present invention.

FIG. 4 is a flowchart showing a misfire state determination control executed by the combustion diagnosis device for the internal combustion engine according to this embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 to 4 illustrate a combustion diagnosis device 10 for an internal combustion engine according to this embodiment of the present invention. Identical components have been allocated identical reference numerals and have identical names and functions. Accordingly, detailed description of these components will not be repeated.

As shown in FIG. 1, a diesel engine (internal combustion engine) 20 according to this embodiment is four cylinders diesel engine that includes four cylinders 21a to 21d. In each cylinder 21a to 21d, an injector 22 that injects the fuel directly into a combustion chamber is provided respectively.

The injector 22 is a solenoid-controlled fuel injection valve comprising a fuel injection nozzle 23 provided with a nozzle hole for injecting the pressurized fuel into the combustion chamber of each cylinder 21a to 21b, a nozzle needle (not shown) slidably received in the fuel injection nozzle 23, and a solenoid valve (not shown) for moving the nozzle needle toward the opening direction. The injector 22 actuates the solenoid valve in accordance with the output control signals (electric pulse) from the ECM 50, to be described bellow, so that the proper quantity of the pressurized fuel being injected into the combustion chamber of each cylinder 21a to 21d. Further, the injector 22 is connected to a common-rail 11 via a fuel injection pipe 24.

The common-rail 11 accumulates the pressurized fuel that is supplied from a high-pressure supply pump 12, and distributes the accumulated fuel to the injector 22 via the fuel injection pipe 24. Further, fuel pressure (common-rail pressure), which is accumulated in the common-rail 11 corresponds to the injection pressure of the fuel, is detected by a fuel pressure sensor 13 and being outputted to the ECM50.

The high-pressure supply pump 12 includes a feed pump (not shown) for feeding the fuel from a fuel tank, a solenoid valve (not shown) for adjusting the discharge rate of the pressurized fuel supplied to the common-rail 11, and so on. Further, as shown in FIG. 1, a fuel temperature sensor 14 is provided on the high-pressure supply pump 12. The sensing value of the fuel temperature sensor 14 is outputted to the ECM 50.

As shown in FIG. 1, an intake manifold 16 into which fresh air (intake air) is introduced by opening an intake valve (not shown) via an intake passage 15 is connected to an intake duct of each cylinder 21a to 21d, and an exhaust manifold 18 into which exhaust gas is discharged by opening an exhaust valve (not shown) via an exhaust passage 17 is connected to the exhaust duct of each cylinder 21a to 21d.

As shown in FIG. 1, a air cleaner 30, a mass air flow sensor 31 provided with an intake air temperature sensor 31a, a compressor 32a provided in a turbocharger 32, and an intercooler 33 are interposed on an upstream side of the intake passage 15.

As shown in FIG. 1, a air cleaner 30, a turbine 32b provided in the turbocharger 32, an exhaust throttle valve 35, and DPF 36a provided in an exhaust gas purification device 36 are interposed on an upstream side of the exhaust passage 17.

Further, as shown in FIG. 1, the intake manifold 16 and the exhaust manifold 18 are connected by an EGR passage 37, and an EGR cooler 38 and an EGR valve 39 are provided in the EGR passage 37.

As shown in FIG. 1, the combustion diagnosis device 10 for the internal combustion engine according to this embodiment includes an engine speed sensor 40, an accelerator opening sensor 41, a vehicle speed sensor 42, a coolant temperature sensor 43, and an EGR position sensor 44. In this embodiment, these sensors are electrically connected to the ECM 50, to be described bellow.

Next, based on FIGS. 1 and 2, the ECM 50 according to this embodiment of the present invention will be described. The ECM 50 performs various controls on the diesel engine 20, and is constituted by conventional components such as a CPU, a ROM, an input port, an output port, and so on. Further, output signals from the engine speed sensor 40, the accelerator opening sensor 41, the vehicle speed sensor 42, the coolant temperature sensor 43, the EGR position sensor 44, and so on are subjected to A/D conversion and then input into the ECM50.

Further, as shown in FIG. 2, the ECM 50 includes, as a part of the functional element thereof, an injector circuit failure determination unit 51, a rotational fluctuation deviation time calculation unit (rotational fluctuation calculation means) 52, a FCCB control unit 53, a fuel injection timing determination unit (combustion state determination means) 54, and a misfire state determination unit (combustion state determination means) 55. In this embodiment, these functional elements are included in the ECM 50 as integrated hardware, but any part thereof can be provided as separate hardware.

The injector circuit failure determination unit 51 determines a failure of the injector 22. More specifically, the injector circuit failure determination unit 51 includes a circuit diagnosis function that determines the failure of the injector 22 in accordance with detect or non-detect of the electrical signals outputted from an electrical circuit (not shown) of the injector 22.

The rotational fluctuation deviation time calculation unit 52 calculates the deviation time of the rotational fluctuation of each cylinder 21a to 21d. More specifically, the rotational fluctuation deviation time calculation unit 52 uses the engine speed sensor 40 for detecting the number of the toothed gears provided on a flywheel (not shown), and measuring the interval time of the count signals. Further, the rotational fluctuation deviation time calculation unit 52 calculates the rotational fluctuation T₃ (=T₂−T₁) of each cylinder 21a to 21d by subtracting a rotational speed fluctuation time T₁, which is detected during the expansion stroke after the top dead center, from a rotational speed fluctuation time Tz, which is detected around the top dead center. Further, the rotational fluctuation deviation time calculation unit 52 is configured to calculate an average rotational fluctuation AVET₃ (=ΣT_k/4) of each cylinder 21a to 21d based on the calculated rotational fluctuation T₃. Furthermore, the rotational fluctuation deviation time calculation unit 52 calculates the deviation time of the rotational fluctuation T₄ (=T₃-AVET₃) of each cylinder 21a to 21d by subtracting the average rotational fluctuation AVET₃ from the calculated rotational fluctuation T₃.

In this embodiment, the deviation time of the rotational fluctuation T₄, which is detected around the top dead center, is calculated by measuring any range of the interval time when the cylinders 21a to 21d are positioned around the top dead center prior to the fuel injection. Further, the rotational speed fluctuation time T₁, which is detected during the expansion stroke after the top dead center, is calculated by measuring any range of the interval time when the rotational speed after explosion is expected to become a peak value.

The FCCB control unit 53 calculates the correction amount for the injection quantity Q. that corrects the fluctuation of the fuel injection in each cylinder 21a to 21d. Further, the FCCB control unit 53 corrects the fuel injection quantity by adding the calculated correction amount for the injection quantity Q_n to a base injection quantity Q. More specifically, in the FCCB control unit 53, a map (not shown) representing the relationship between the deviation time of the rotational fluctuation T₄ and the correction amount for the injection quantity Q_n, is stored in advance. The FCCB control unit 53 is configured to calculate the correction amount for the injection quantity Q_n by reading a value corresponding to the deviation time of the rotational fluctuation T₄ from the map. Further, the FCCB control unit 53 is configured to correct the base fuel injection of each cylinder 21a to 21d in accordance with the calculated correction amount for the injection quantity Q_n. Furthermore, when the correction amount for the injection quantity Q_n reaches an upper limit correction threshold value (to be referred to hereafter as an upper limit threshold value) Q_m, the FCCB control unit 52 maintains the correction amount for the injection quantity Q_n at the correction amount for the injection quantity Q_n−1 that is previously calculated.

The fuel injection timing determination unit 54 determines an advanced angle or a retarded angle of the fuel injection timing that representing the combustion state of each cylinder 21a to 21d. More specifically, in a case when the correction amount for the injection quantity Q_n calculated by the FCCB control unit 53 reaches the upper limit threshold value Q_m and the deviation time of the rotational fluctuation T₄ calculated by the rotational fluctuation deviation time calculation unit 52 is more than a determination threshold value of the advanced angle injection timing K₁ (to be referred to hereafter as a determination threshold value K₁)(T₄>K₁), the fuel injection timing of the determination-target cylinder is determined as an advanced angle side. Further, in a case when the deviation time of the rotational fluctuation T₄ is less than a determination threshold value of the retarded angle injection timing K₂ (to be referred to hereafter as a determination threshold value K₂) (T₄<K₂), the fuel injection timing of the determination-target cylinder is determined as a retarded angle side. Furthermore, in a case when the deviation time of the rotational fluctuation T₄ is equal to or more than the determination threshold value K₂ and less than or equal to the determination threshold value K₁ (K₂<=T₄<=K₁), the fuel injection timing of the determination-target cylinder is determined as a normal state. In this embodiment, the determination threshold value K₂ is smaller than the determination threshold value K₁.

In this embodiment, the deviation time of the rotational fluctuation T₄, which is used in the determination of the fuel injection timing, may be replaced by integrating and averaging more than one deviation time of the rotational fluctuation T₄ being calculated during plurality of the combustion cycles (for example, 6 cycles), and the fuel injection timing may be determined in accordance with the averaged deviation time of the rotational fluctuation. In this case, the averaged deviation time of the rotational fluctuation, which may be used in the later determinations, can be calculated from the moving average.

The misfire state determination unit 55 determines occurrence or nonoccurrence of the misfire that representing the combustion state of each cylinder 21a to 21d. More specifically, in a case when the correction amount for the injection quantity Q_n calculated by the FCCB control unit 53 reaches the upper limit threshold value Q_m and the deviation time of the rotational fluctuation T₄ calculated by the rotational fluctuation deviation time calculation unit 52 is less than a determination threshold value of misfire K₃ (to be referred to hereafter as a determination threshold value K₃) (T₄<K₃), the combustion state of the determination-target cylinder is determined that the misfire is caused. Further, in a case when the deviation time of the rotational fluctuation T₄ is equal to or more than the determination threshold value K₃ (T₄=>K₃), the combustion state of the determination-target cylinder is determined that the misfire is not caused. In this embodiment, the determination threshold value K₃ is smaller than the determination threshold value K₂.

In this embodiment, the deviation time of the rotational fluctuation T₄, which is used in the determination of the misfire state, may be replaced by integrating and averaging more than one deviation time of the rotational fluctuation T₄ being calculated during plurality of the combustion cycles (for example, 6 cycles), and the occurrence or nonoccurrence of the misfire may be determined in accordance with the averaged deviation time of the rotational fluctuation. In this case, the averaged deviation time of the rotational fluctuation, which may be used in the later determinations, can be calculated from the moving average.

In the combustion diagnosis device 10 according to this embodiment of the present invention, having the configuration described above, the following control is performed in accordance with flows shown in FIGS. 3 and 4, for example.

First, a fuel injection timing determination control flow, shown in FIG. 3, will be described. This control flow is started at the same time as the starting of the diesel engine 20 (ON operation of key).

In Step (hereafter, Step will be abbreviated to S) 100, a determination is made by the injector circuit failure determination unit 51 as to whether or not the electrical circuit of the injector 22 is failed due to the disconnection, and so on. When the injector 22 is not failed, the control advances to S110, and when the injector 22 is failed, the control is returned.

In S110, a determination is made as to whether or not the correction control for fuel injection quantity by the FCCB control unit 53 is performed. When the correction control for the fuel injection quantity is performed, the control advances to S120, and when the correction control for the fuel injection quantity is not performed, the control is returned.

In S120, a determination is made as to whether the permissible conditions for the determination of the fuel injection timing are satisfied. The purpose of confirming the permissible conditions for the determination is to prevent the determination errors of the fuel injection timing that may be caused when the operating condition of the diesel engine 20 becomes significantly unstable. As for the permissible conditions that can satisfy the determination of the fuel injection timing, for examples, are when the detected value of the accelerator opening sensor 42 is less than or equal to a predetermined threshold value, when the detected value of the coolant temperature sensor 43 is equal to or more than a predetermined threshold value, when a PTO device (not shown) is not operated, or when a forcible regeneration control of the DPF 36a by the post injection and so on is not performed. When the permissible conditions for the determination of the fuel injection timing are satisfied, the control advances to S130. On the other hand, when the permissible conditions for the determination are not satisfied, the control is returned.

In S130, the fuel injection timing determination unit 54 determines whether or not the correction amount for the injection quantity Q_n, which is calculated by the FCCB control unit 53, is reached the upper limit threshold value Q_m. When the correction amount for the injection quantity Q_n reaches the upper limit threshold value Q_m, the control advances to S 140. On the other hand, when the correction amount of the injection quantity Q_n is less than or equal to the upper limit threshold value Q_m, the control is returned.

In S140, the rotational fluctuation deviation time calculation unit 52 calculates the rotational fluctuation T₃ of each cylinder 21a to 21d by subtracting the rotational speed fluctuation time T₁ detected during the expansion stroke after the top dead center from the rotational speed fluctuation time T₂ detected around the top dead center.

In S150, the rotational fluctuation deviation time calculation unit 52 calculates the average rotational fluctuation AVET₃ of each cylinder 21a to 21d in accordance with the rotational fluctuation T₃ that is calculated in S140.

In S 160, the rotational fluctuation deviation time calculation unit 52 calculates the deviation time of the rotational fluctuation T₄ in each cylinder 21a to 21d by subtracting the average rotational fluctuation AVET₃ calculated in S150 from the rotational fluctuation T₃ calculated in 5140.

From S170 to S210, the fuel injection timing determination unit 54 determines the fuel injection timing of the determination^-target cylinder.

In S170, when the deviation time of the rotational fluctuation T₄ is more than the determination threshold value K₁ (T₄>K₁), the control advances to S180. In 5180, the fuel injection timing determination unit 54 determines the fuel injection timing of the determination-target cylinder as the advanced angle side, and then the control is returned. On the other hand, in S170, when the deviation time of the rotational fluctuation T₄ is less than or equal to the determination threshold value K₁ (T₄=>K₁), the control advances to S190.

In S190, a determination is made as to whether the deviation time of the rotational fluctuation T₄ is less than the determination threshold value K₂. When the deviation time of the rotational fluctuation T₄ is less than the determination threshold value K₂ (T₄<K₂), the control advances to 5200. In S200, the fuel injection timing determination unit 54 determines the fuel injection timing of the determination-target cylinder as the retarded angle side, and then the control is returned. On the other hand, in S190, when the deviation time of the rotational fluctuation T₄ is equal to or more than the determination threshold value K₂ (K₂<=T₄<=K₁), the control advances to S210. In 5210, the fuel injection timing determination unit 54 determines the fuel injection timing of the determination^-target cylinder as normal state, and then the control is returned.

Next, a misfire state determination control flow, shown in FIG. 4, will be described. From S300 to S360 of this control flow is same as S100 to S160 of above mentioned fuel injection timing determination control flow shown in FIG. 3 and, accordingly, will not be described in detailed.

In S360, the rotational fluctuation deviation time calculation unit 52 calculates the deviation time of the rotational fluctuation T₄ in each cylinder 21a to 21d, and then, the misfire state determination unit 55 determines the misfire state of the determination-target cylinder, from S370 to S390.

In S370, when the deviation time of the rotational fluctuation T₄ is less than the determination threshold value K₃ (T₄<K₃), the control advances to S380. In S380, the misfire state determination unit 55 determines that the misfire is caused in the determination-target cylinder, and then the control is returned. On the other hand, in S370, when the deviation time of the rotational fluctuation T₄ is equal to or more than the determination threshold value K₃ (T₄=>K₃) the control advances to S390. In S390, the misfire state determination unit 55 determines that the misfire is not caused in the determination-target cylinder, and then the control is returned.

By employing the configuration described above, actions and effects such as the following can be obtained with the combustion diagnosis device 10 for the internal combustion engine according to this embodiment of the present invention.

The fuel injection timing determination unit 54 determines the fuel injection timing of the determination-target cylinder in accordance with the deviation time of the rotational fluctuation T₄ calculated by the rotational fluctuation deviation time calculation unit 52 when the correction amount for the injection quantity Q_n of the FCCB control unit 53 is reached the upper limit threshold value Q_m.

Therefore, even when the correction amount for the injection quantity Q_n calculated by the FCCB control unit 53 becomes large amount due to the effects of disturbances on the diesel engine 20, the determination of the fuel injection timing is executed in accordance with the rotational fluctuation deviation time T₄, and as a result, the fuel injection timing of the determination-target cylinder can be accurately determined by removing the effects of disturbances.

Further, the misfire state determination unit 55 determines the misfire state of the determination-target cylinder in accordance with the deviation time of the rotational fluctuation T₄ calculated by the rotational fluctuation deviation time calculation unit 52 when the correction amount for the injection quantity Q_n of the FCCB control unit 53 is reached the upper limit threshold value Q_m.

Therefore, even when the correction amount for the injection quantity Q_n calculated by the FCCB control unit 53 becomes large amount due to the effects of disturbances on the diesel engine 20, the determination of the misfire state is executed in accordance with the rotational fluctuation deviation time T₄, and as a result, the misfire state of the determination-target cylinder can be accurately determined by removing the effects of disturbances.

Note that the present invention is not limited to the embodiment described above and may be amended appropriately within a scope that does not depart from the spirit of the present invention.

For example, the diesel engine 20 is not limited to 4 cylinders, but single cylinder engine or the engine that having more cylinders can be also used. Further, the determination of the combustion state for each cylinder 21a to 21d is not limited to the fuel injection timing or the misfire state of the determination-target cylinder, but for example a fuel injection quantity of the determination-target cylinder can be determined in accordance with a fuel injection period and a lift amount of the core valve in the injector 22 that may be detected by sensor.

EXPLANATION OF REFERENCE NUMERALS

• • 10 combustion diagnosis device
  • 20 diesel engine (internal combustion engine)
  • 40 engine speed sensor (engine rotational speed detection means)
  • 52 rotational fluctuation deviation time calculation unit (rotational fluctuation calculation means)
  • 53 FCCB control unit (injection correction amount calculation means)
  • 54 fuel injection timing determination unit (combustion state determination means)
  • 55 misfire state determination unit (combustion state determination means)

Claims

1-6. (canceled)

7. A combustion diagnosis device for an internal combustion engine having a plurality of cylinders, comprising:

an engine rotational speed detection means for detecting the rotational speed of each cylinder of the internal combustion engine;

an injection correction amount calculation means for calculating the amount of correction for the fuel injection of each cylinder in accordance with the engine rotational speed detection means;

a rotational fluctuation calculation means for calculating the rotational fluctuation of each cylinder in accordance with the engine rotational speed detection means; and

a combustion state determination means for determining the combustion state of a determination-target cylinder in accordance with the rotational fluctuation when the correction amount calculated by the injection correction amount calculation means reaches an upper limit threshold value.

8. The combustion diagnosis device for the internal combustion engine according to claim 7, characterized in that when the rotational fluctuation is larger than a determination threshold value of advanced angle injection timing, the combustion state determination means determines the injection timing of the determination-target cylinder as an advanced angle side.

9. The combustion diagnosis device for the internal combustion engine according to claim 8, characterized in that when the rotational fluctuation is smaller than a determination threshold value of retarded angle injection timing, the combustion state determination means determines the injection timing of the determination-target cylinder as a retarded angle side, and the determination threshold value of retarded angle injection timing is smaller value than the determination threshold value of advanced angle injection timing.

10. The combustion diagnosis device for the internal combustion engine according to claim 7, characterized in that when the rotational fluctuation is smaller than a determination threshold value of misfire state, the combustion state determination means determines that a misfire is caused in the determination-target cylinder, and when the rotational fluctuation is equal to or more than the determination threshold value of misfire state, the combustion state determination means determines that the misfire is not caused in the determination-target cylinder.

11. The combustion diagnosis device for the internal combustion engine according to claim 8, characterized in that when the rotational fluctuation is smaller than a determination threshold value of misfire state, the combustion state determination means determines that a misfire is caused in the determination-target cylinder, and when the rotational fluctuation is equal to or more than the determination threshold value of misfire state, the combustion state determination means determines that the misfire is not caused in the determination-target cylinder.

12. The combustion diagnosis device for the internal combustion engine according to claim 9, characterized in that when the rotational fluctuation is smaller than a determination threshold value of misfire state, the combustion state determination means determines that a misfire is caused in the determination-target cylinder, and when the rotational fluctuation is equal to or more than the determination threshold value of misfire state, the combustion state determination means determines that the misfire is not caused in the determination-target cylinder.

13. The combustion diagnosis device for the internal combustion engine according to claim 7, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

14. The combustion diagnosis device for the internal combustion engine according to claim 8, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

15. The combustion diagnosis device for the internal combustion engine according to claim 9, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

16. The combustion diagnosis device for the internal combustion engine according to claim 10, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

17. The combustion diagnosis device for the internal combustion engine according to claim 11, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

18. The combustion diagnosis device for the internal combustion engine according to claim 12, further comprising a fuel injection amount correction means for correcting a base fuel injection of each cylinder in accordance with the correction amount calculated by the injection correction amount calculation means.

19. The combustion diagnosis device for the internal combustion engine according to claim 13, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.

20. The combustion diagnosis device for the internal combustion engine according to claim 14, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.

21. The combustion diagnosis device for the internal combustion engine according to claim 15, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.

22. The combustion diagnosis device for the internal combustion engine according to claim 16, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.

23. The combustion diagnosis device for the internal combustion engine according to claim 17, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.

24. The combustion diagnosis device for the internal combustion engine according to claim 18, characterized in that when the correction amount calculated by the injection correction amount calculation means is larger than an upper limit correction threshold value, the fuel injection amount correction means corrects the base fuel injection of each cylinder by previous correction amount.